1. Field
The subject invention relates to plasma processing chambers and, in particular, to a coating for an electrostatic chuck of a plasma processing chamber, which enhances the performance of the chuck in the presence of active plasma species.
2. Related Art
In plasma processing chambers, an electrostatic chuck (ESC) is often used to support the processed substrate inside the chamber. In certain plasma chambers, such as plasma etch chambers, the ESC may also function as an electrode, coupled to either ground or RF potential. During processing, at least part of the ESC is exposed to the plasma and is attacked by the active species within the plasma, such as halogen plasma of CF4, Cl2, etc. Additionally, the ESC is exposed to mechanical abrasion from the substrates it supports. Finally, in some cases various plasma cleaning procedures are employed, wherein the interior of the chamber is cleaned using plasma species. In many such cleaning procedures no wafer is present on the ESC, such that the entire substrate-supporting surface of the ESC is exposed to plasma.
Various coatings have been proposed and tested in the prior art for protecting plasma chamber parts from plasma erosion. One typical application is the plasma sprayed (PS) Y2O3 or Al2O3 on ESC base that could be metal, alloy or ceramics. Plasma sprayed Al2O3 coated ESC has been used for a quite long time, but it introduces the risk of aluminum contamination of the processed substrate. On the other hand, plasma sprayed Y2O3 ESC has a soft surface which is easily damaged by the substrates, creating particles and contamination of the processed substrate.
Generally, Yttria (Y2O3) coating is believed to be promising; however, it has been very difficult to find a process that results in good coating, especially one that does not crack or generate particles. For example, there have been proposals to use plasma spray to coat parts made of metal, alloy or ceramic. However, conventional plasma spray Y2O3 coating is formed by sprayed Y2O3 particles, and generally results in a coating having high surface roughness (Ra of 4 micron or more) and relatively high porosity (volume fraction is above 3%). The high surface roughness and porous structure makes the coating susceptible to generation of particles, which may contaminate the substrate being processed.
Other proposals for forming Yttria coating involve using chemical vapor deposition (CVD), physical vapor deposition (PVD), ion assisted deposition (IAD), ionized metal plasma (IMP), active reactive evaporation (ARE), sputtering deposition, and plasma immersion ion process (PIIP). However, all these deposition processes have some technical limitations such that they can not be actually used to scale up for the deposition of thick coating on the chamber parts for the plasma attack protections. For instance, CVD of Y2O3 can not be carried out on substrates that cannot sustain temperatures above 600 C, which excludes the deposition of plasma resistant coating on chamber parts that are made of aluminum alloys. PVD process, such as evaporation, can not deposit thick ceramic coating because of their poor adhesion to substrate. Other deposition processes can not deposit thick coating either due to the high residual stress and poor adhesion (such as sputtering deposition, ARE and IAD) or the very low deposition rate (such as sputtering deposition, IMP and PIIP). Therefore, so far no satisfactory film has been produced, that would have good erosion resistance, while generating low or no particles and can be made thick without cracking or delamination.
In view of the above-described problems in the art, a solution is needed for a coated ESC with coating that resists plasma species attack and does not generate particle or cracks. The coating should have acceptable roughness and porosity values, enough hardness and good thermal conductivity, so that it could provide long service life. The process for fabricating the coating should allow thick coating without being susceptible to cracking or delamination.